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Chemical analysis of cell wall and energy digestibility in growing pigs
Animal Feed Science and Technology, 32 ( 1991 ) 55-61
55
Elsevier Science Publishers B.V., Amsterdam
Chemical analysis of cell wall and energy digestibility in growing pigs I.J. Vervaeke ~, H. Graham 2"*, N.A. Dierick ~, D.I. Demeyer' and J.A. Decuypere' ~Onderzoekscentrum Voeding, Veeteelt en Vleestechnologie, Proefhoevestraat, 10. 9230 Melle (Belgium) 2Department of Animal Nutrition and Management, Box 7024, S 75007 Uppsala (Sweden)
ABSTRACT Vervaeke, l.J., Graham, H., Dierick, N.A., Demeyer, D.I. and Decuypere, J.A., 199 I. Chemical analysis of cell wall and energy digestibility in growing pigs. Anita. Feed Sci. Technol.. 32:55-6 I. Ileal and faecal fibre digestibility was studied in pigs, with six diets containing increasing levels (1.5-9%) of beet pulp, alfalfa and wheat bran. The apparent digestibility of fibre was assessed from the crude fibre (CF), the neutral and acid detergent fibre (NDF, ADF) and the non-starch polysaccharides (NSP). The analytical methods employed gave clearly different figures for fibre content in the diets and their respective ileal and faecal residues. Crude fibre, NDF and ADF underestimated fibre degradation in the hindgut by more than 100%when compared with NSP values. Xylose and glucose polymers were the most resistant to digestion. At the ileal level, the NDF overestimated fibre digestibility. Solubilization, particularly of uronic acid residues, anterior to the caecum was apparent. Solubilized NSP glucose, on the other hand. was substantiallydegraded in the small intestine.
INTRODUCTION
Fibre in pig nutrition was extensively reviewed by Low ( 1985 ), who discussed dietary fibre in relation to digestive processes in the small intestine, volatile fatty acids (VFA) supply, nutrient digestibility measured overall, transit time, and effects measured on the whole animal, such as voluntary feed intake, growth and body composition. Dierick et al. (1989) reviewed fibre degradation and VFA as a source of energy, and concluded that the importance of fibre fermentation in pigs should not be evaluated in isolation but as an integrated part of the overall energy supply to the pig. High fibre levels do not change the total number of microorganisms but cause a shift to more fibre-degrading organisms. As the definition and analytical determination of the fibre complex is of crucial importance in the estimation and nutritional *Present address: Finnfeeds International Ltd., Forum House, 41-51 Brighton Road, Redhill, RHI 6YS, Gt. Britain.
0377-8401/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
56
I.J.VERVAEKEETAL.
evaluation of fibre degradation at the ileal and faecal level, several analytical methods for fibre determination were compared in the present study. Gravimetric methods such as the crude fibre analysis (van Soest, 1982), the use of detergents (van Soest, 1982 ) and the gravimctric determination of soluble and insoluble fibre (Asp et al., 1983 ) provide little or no information on the chemical composition of the fibre. Consequently, they are not suitable for the study of the relationship between fibre composition, fermentation intensity in the gastrointestinal tract and energy supply. Modern chemical methods determine the neutral sugars from non-starch polysaccharides by gas chromatography, the uronic acid residues by decarboxylation or spectrophotometry and Klason lignin gravimetrically (Theander and Aman, 1979). Graham (1988 ) also claimed that a better understanding of the complex effects of fibre on assimilation in pigs would result only from more detailed knowledge of the chemical and physical properties of fibre present in diets. EXPERIMENTAL Six ileal cannulated female pigs (20 kg liveweight) were offered six diets ( D 10-D 15 ) in a 2 × (3 X 3 ) Latin square arrangement. They were fed every 2 h with an automatic feeding system. The composition of the diets was characterized by: (i) a similar calculated net energy content; (ii) a digestible crude protein (DCP) content of 13%; (iii) a minimum cereal level of 25% and a manioc level of at least 10%; (iv) increasing fibre levels from D10 to D15 principally obtained by adding 1.5, 3.0, 4.5, 6.0, 7.5 and 9.0% of dried sugar beet pulp, wheat bran and alfalfa; (v) supplementation with 0.5% celite as a marker. Ileal contents were collected every 30rain from 09:00 to 17:00 h, 3 days per week, by free outflow to plastic bags, and pooled daily for each pig before freeze drying. Thereafter, samples were pooled for each diet. Faeces were collected twice per day, frozen immediately, later dried at 60 °C and pooled. Finally, six diets, six ileal and six faecal samples were analysed for CF, NDF, ADF and TDF (Theander and Aman, 1979 ). RESULTSAND DISCUSSION
In vivo experiments Data from the fibre analyses of the six diets and the corresponding pooled ileal and faecal samples are given in Table 1. The CF and NDF levels are quoted as percentages of total dietary fibre (TDF). From comparison of the results, it is clear that the proportions of the various analytical fibre parameters differ between diets and between their ileal and faecal residues. At the dietary level, NDF and TDF are reasonably similar, while CF is 35% of the
FIBREDIGESTIBILITYIN PIGS
57
TABLE 1 Dietary, ileal and faecal fibre contents (% DM ) Diets D 10-D 15 D10
DII
DI2
DI3
DI4
DI5
Dietary samples CF ADF NDF NSP Klason lignin TDF KMnO4 lignin
5.26 8.05 14.87 14.21 1.55 i 5.76 1.65
6.05 10.21 15.81 14.37 1.61 ! 5.98 2.29
6.85 10.07 18.00 16.87 2.05 18.92 4.02
9.63 12.64 21.02 18.91 2.61 21.52 3.38
9.09 13.30 24.07 21.23 3.21 24.44 3.58
8.91 13.30 23.98 19.57 3.19 22.76 3.90
Percent of TDF CF NDF
33.37 94.35
37.86 98.94
36.21 95.14
44.75 97.67
37.19 98.49
39.15 105.36
Ileal samples CF ADF NDF NSP Klason iignin TDF KMnO4 lignin
15.00 21.47 34.50 38.74 4.66 43.40 2.71
14.35 22.57 32.69 34.99 5.37 40.36 2.24
15.55 23.09 34.12 38.87 5.86 44.73 1.99
18.59 28.17 40.27 37.45 7.29 44.74 4.49
18.10 27.29 41.43 44.35 7.04 51.39 3.59
16.16 24.98 37.68 36.26 6.43 42.69 4.86
Percent of TDF CF NDF
34.56 79.49
35.55 80.99
34.76 76.28
41.55 90.00
35.22 80.61
37.85 88.26
Faecal samples CF ADF NDF NSP Klason lignin TDF KMnO4 lignin
21.30 33.21 47.72 30.55 10.74 41.29 6.24
17.18 30.17 40.79 24.82 l 1.42 36.24 5.77
21.50 36.25 45.59 30.01 12.69 42.70 7.68
21.30 36.81 44.86 29.75 17.23 46.98 9.29
20.86 33.33 49.74 30.79 15. ! 5 45.94 7.41
18.16 28.39 38.76 24.44 12.60 37.04 7.46
Percent of TDF CF NDF
51.78 115.57
47.41 112.56
50.35 106.77
45.34 95.48
45.41 108.27
49.03 104.64
CF, crude fibre; ADF, acid detergent fibre; NDF, neutral detergent fibre; NSP, non-starch polysaccharides; TDF, total dietary fibre (NSP + Klason lignin ).
TDF content. Klason lignin contents at ileal and faecal levels exceed the KMnO4 lignin, presumably because of the presence of variable amounts of non-lignin components such as waxes, cutin, tannins and glycoproteins in the former (Graham, 1988 ). At the faecal level, a relatively important decrease
58
I.J. VERVAEKEETAL.
in NSP content and an enrichment of the Klason lignin again changed relative concentrations of the various fibres. Concerning fibre degradation (Table 2), it is noticeable that the ileal apparent degradability values for CF, ADF, TDF and NSP were in the same range for each diet, but lower than the N D F digestibility, probably because of partial solubilization of the NDF fraction in the small intestine. The faecal NSP degradability greatly exceeded the other fibre degradability values and was similar for all the diets, while CF and ADF degradability values differed more among diets. The soluble NSP fraction was enriched by nearly 19% at the ileum and the insoluble NSP fraction degraded by approximately 21% (Table 3 ). This solubilization could possibly lead to an underestimation of fibre degradation capacity in the small intestine if inappropriate methods were used. It is noteworthy that 18% of the total dietary NSP fraction was degraded precaecally. According to Graham ( 1988 ), a significant degradation of some dietary fibres can occur prior to the ileum, probably as a result of bacterial activity, and this should facilitate a more complete digestion of other nutrients in the upper part of the tract. TABLE 2
Ileal and faecal apparent digestibility of fibre (%) DI0
Dll
DI2
DI3
DI4
Dl5
6.1 12.2 23.6 9.4 10.3 65.7
20.8 20.2 30.9 15.6 18.7 65.1
19.4 18.6 32.7 16.0 18.2 62.2
24.1 12.4 24.7 18.2 22.2 58.9
14.8 12.2 26.3 10.0 10.6 56.8
13.8 10.8 25.4 10.9 12.0 53.3
29.8 28.4 45.0 54.6 62.7 85.6
49.2 47.2 53.9 59.5 69.1 84.0
44.6 30.5 55.3 60.2 62.6 83.0
44.0 40.0 56.1 55.1 67.0 81.0
51.3 46.9 56.2 60.1 69.4 79.2
49.3 41.6 55.8 53.0 65.9 74.6
23.7 16.2 21.4 45.2 52.4 19.9
28.4 21.0 23.0 43.9 50.4 18.9
25.2 17.9 22.6 44.2 50.4 20.8
19.9 27.6 31.4 35.9 44.8 22.1
36.5 34.7 29.9 50.1 58.8 22.4
30.5 30.8 30.4 42.1 63.9 21.3
Ileal CF ADF NDF TDF
NSP OM
Faecal CF ADF NDF TDF
NSP OM
Faecal-ileal CF ADF NDF TDF
NSP OM
CF, crude fibre; ADF, acid detergent fibre; NDF, neutral detergent fibre; TDF, total dietary fibre; NSP, non-stareh polysaccharides; OM, organic matter.
FIBREDIGESTIBILITYIN PIGS
59
TABLE 3 Dietary composition and ileal and faecal digestibility (% DM) of soluble (S) and insoluble ( IS ) nonstarch polysaccharides (NSP): comparison of diets DI0 Diet Content
Ileal Content
Digestible
Faecal Content
Digestible
DII
DI2
D13
D14
D15
Mean
SD
S IS Total
2.3 11.9 14.2
2.1 12.3 14.4
2.4 14.5 16.9
2.7 16.3 19.0
2.8 18.4 21.2
3.2 16.4 19.6
S IS Total S IS Total
7.5 31.1 38.7 -11.6 14.4 10.3
6.6 28.4 35.0 -3.6 22.5 18.7
8.0 30.9 38.9 -18.9 24.3 18.2
7.8 29.7 37.5 - 1 5 .0 28.2 22.2
8.6 35.8 44.4 -30.0 16.9 10.6
9.1 27.2 36.3 -34.8 21.1 12.0
-19.1 21.3 17.9
11.6 5.0 5.0
S IS Total S IS Total
1.2 29.4 30.6 90.9 57.4 62.7
1.2 23.6 24.8 89.7 65.6 69.1
1.1 28.9 30.0 91.6 64.8 68.6
1.1 28.7 29.8 91.6 63.7 67.0
1.3 29.5 30.8 90.3 66.0 69.4
1.2 23.2 24.4 89.3 54.2 65.9
90.6 61.9 67.1
0.9 4.9 2.5
The total faecal NSP digestibility was between 62 ( D I 0 ) and 69% (D14). Differences were generally larger at the ileal than at the faecal level, confirming the general statement that ileal results are characterized by a higher variability than faecal data. Table 4 summarizes the dietary levels, ileal and faecal digestibility of the soluble and insoluble NSP monomers. Rhamnose and mannose residues, present in the diets at less than 1%o,are not mentioned. Arabinose, xylose, galactose, glucose and uronic acid concentrations were respectively 2.8, 3.0, 1.4, 6.7 and 2.8% of the dry matter content with a soluble fraction of less than 1%o.The general increase of arabinose and uronic acid residues from D I0 to D 15 is mainly related to the higher beet pulp content. The xylose increase on the other hand originated from a higher wheat bran or cereal level. According to the ileal digestibility data (Table 3) the soluble NSP monomers and particularly the uronic acids, were enriched (negative digestibility ). Soluble glucose, presumably from cereal mixed-linked fl-glucans, was degraded by 50%. The insoluble NSP fraction was degraded by 21%0 in the ileum with the highest level from uronic acids and a lower one from xylose residues. Soluble undegraded monomers are transported to the caecum. At the faecal level, only 10% of each soluble NSP component was recovered, suggesting a non-specific and high fermentative capacity of soluble substrates by the microflora. The
60
I.J. VERVAEKEET AL.
TABLE 4 Non-starch polysaccharides: dietary composition, ileal and faecal digestibility (%) NSP components Arabinose
Xylose
Dietary level (% DM ) Total 2 2.753 (1.86;3.82)
3.02 (4.03;2.42)
lleal digestibility (%) Total 7.034 (-4.4; 14.3)
11.0 (1.8; 19.8)
Faecal digestibility (%) Total 74.7 (70.2, 78.0)
52.9 (44.7; 57.1 )
Galactose 1.41 (1.13;1.99)
9.0 (-9.3; 18)
82.4 (75.1; 89.9)
Glucose 6.76 (5.64;7.84)
Uronic acids 2.80 (1.58;3.65)
Total NSP m 17.53 (14.21;21.33)
24.5 (14.6;32.7)
28.0 (-8.1~ 36.3)
17.9 (10.3;26.3)
59.9 (53.3; 64.1 )
81.8 (76.5: 84.9)
67.1 (62.7; 69.4)
Total NSP (rhamnose and mannose included ). aSoluble and insoluble. ~Mean content of D l 0 - D l 5, with range given in parentheses. 4Average digestion coefficient (DC) with range given in parentheses.
digestibility coefficients of the residues from insoluble non-starch polysaccharide, however, varied from 53% for xylose and 60% for glucose to 75% for arabinose and 82% for the uronic acids. These data suggest that cereal hemicelluloses and cellulose are the most resistant polysaccharides in cereals. From our in vivo experiments (Vervaeke et al., 1989) it was concluded that organic matter degradation in the hindgut occurs principally and very quickly in the caecum and proximal colon. These results were in agreement also with the highest in vitro VFA production rates with inoculum from caecal and colon contents of slaughtered pigs. From these experiments, it can be expected that the transit time of the digesta in the large intestine should be of secondary importance to the total hindgut digestive capacity of carbohydrates, as composition of the undegraded insoluble NSP fraction is apparently the main factor limiting the fermentation; moreover, a lower water activity in the distal segments of the large intestine would tend to limit microbial attack. CONCLUSION
Beet pulp, alfalfa and wheat bran were simultaneously included in six diets at levels from 1.5 to 9.0% each in order to obtain significant differences in ileal and large intestinal digestion. Differences in CF, NDF, ADF and TDF were larger, however, at the ileal and faecal level than at the dietary level. The CF data represent only a small part of the total dietary fibre fraction and
FIBRE DIGESTIBILITY IN PIGS
61
consequently underestimate the fibre digestive capacity of the pig substantially. The NDF and ADF faecal and hindgut digestibility values were substantially lower than the NSP digestibility. The solubilization of non-starch polysaccharides, particularly of uronic acid residues, in the small intestine was apparent. The faecal data show that xylose and glucose polymers are the NSP most resistant to digestion. ACKNOWLEDGEMENTS
This work, which was supported by the IWONL, Brussels, benefited from a fellowship award under an OECD project on Food Production and Preservation.
REFERENCES Asp, N.G., Johansson, C.G., Hollmer, H. and Siljestr~im, M., 1983. Rapid enzymatic assay of insoluble and soluble dietary fibre. J. Agric. Food. Chem., 31: 476-482. Dierick, M.A., Vervaeke, l.J., Demeyer, D.I. and Decuypere, J.A., 1989. Approach to the energetic importance of fibre digestion in pigs. I. Importance of fermentation in overall energy supply. Anim. Feed Sci. Technol., 23: 141-167. Graham, H., 1988. Dietary fibre concentration and assimilation in swine. Anim. Plant Sci.. 1 : 76-80. Low, A.G., 1985. Role of dietary fibre in pig diets. In: W. Haresign and D.E. Cole (Edilors). Recent Advances in Animal Nutrition. Butterworths, London, pp. 87-112. Theander, O. and Aman, P., 1979. Studies on dietary fibres. 1. Analysis and chemical characterisation of water-soluble and water-insoluble dietary fibres. Swed. J. Agric. Res., 9: 97106. Van Soest, P.. 1982. Nutritional Ecology of the Ruminant. O & B Books, Corvallis, OR. 374 pp. Vervaeke, l.J., Dierick, N.A., Demeyer, D.I. and Decuypere, J.A., 1989. Approach to the energetic importance of fibre digestion in pigs. II. An experimental approach to hindgut digeslion. Anim. Feed Sci. Technol., 23: 169-194.
55
Elsevier Science Publishers B.V., Amsterdam
Chemical analysis of cell wall and energy digestibility in growing pigs I.J. Vervaeke ~, H. Graham 2"*, N.A. Dierick ~, D.I. Demeyer' and J.A. Decuypere' ~Onderzoekscentrum Voeding, Veeteelt en Vleestechnologie, Proefhoevestraat, 10. 9230 Melle (Belgium) 2Department of Animal Nutrition and Management, Box 7024, S 75007 Uppsala (Sweden)
ABSTRACT Vervaeke, l.J., Graham, H., Dierick, N.A., Demeyer, D.I. and Decuypere, J.A., 199 I. Chemical analysis of cell wall and energy digestibility in growing pigs. Anita. Feed Sci. Technol.. 32:55-6 I. Ileal and faecal fibre digestibility was studied in pigs, with six diets containing increasing levels (1.5-9%) of beet pulp, alfalfa and wheat bran. The apparent digestibility of fibre was assessed from the crude fibre (CF), the neutral and acid detergent fibre (NDF, ADF) and the non-starch polysaccharides (NSP). The analytical methods employed gave clearly different figures for fibre content in the diets and their respective ileal and faecal residues. Crude fibre, NDF and ADF underestimated fibre degradation in the hindgut by more than 100%when compared with NSP values. Xylose and glucose polymers were the most resistant to digestion. At the ileal level, the NDF overestimated fibre digestibility. Solubilization, particularly of uronic acid residues, anterior to the caecum was apparent. Solubilized NSP glucose, on the other hand. was substantiallydegraded in the small intestine.
INTRODUCTION
Fibre in pig nutrition was extensively reviewed by Low ( 1985 ), who discussed dietary fibre in relation to digestive processes in the small intestine, volatile fatty acids (VFA) supply, nutrient digestibility measured overall, transit time, and effects measured on the whole animal, such as voluntary feed intake, growth and body composition. Dierick et al. (1989) reviewed fibre degradation and VFA as a source of energy, and concluded that the importance of fibre fermentation in pigs should not be evaluated in isolation but as an integrated part of the overall energy supply to the pig. High fibre levels do not change the total number of microorganisms but cause a shift to more fibre-degrading organisms. As the definition and analytical determination of the fibre complex is of crucial importance in the estimation and nutritional *Present address: Finnfeeds International Ltd., Forum House, 41-51 Brighton Road, Redhill, RHI 6YS, Gt. Britain.
0377-8401/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
56
I.J.VERVAEKEETAL.
evaluation of fibre degradation at the ileal and faecal level, several analytical methods for fibre determination were compared in the present study. Gravimetric methods such as the crude fibre analysis (van Soest, 1982), the use of detergents (van Soest, 1982 ) and the gravimctric determination of soluble and insoluble fibre (Asp et al., 1983 ) provide little or no information on the chemical composition of the fibre. Consequently, they are not suitable for the study of the relationship between fibre composition, fermentation intensity in the gastrointestinal tract and energy supply. Modern chemical methods determine the neutral sugars from non-starch polysaccharides by gas chromatography, the uronic acid residues by decarboxylation or spectrophotometry and Klason lignin gravimetrically (Theander and Aman, 1979). Graham (1988 ) also claimed that a better understanding of the complex effects of fibre on assimilation in pigs would result only from more detailed knowledge of the chemical and physical properties of fibre present in diets. EXPERIMENTAL Six ileal cannulated female pigs (20 kg liveweight) were offered six diets ( D 10-D 15 ) in a 2 × (3 X 3 ) Latin square arrangement. They were fed every 2 h with an automatic feeding system. The composition of the diets was characterized by: (i) a similar calculated net energy content; (ii) a digestible crude protein (DCP) content of 13%; (iii) a minimum cereal level of 25% and a manioc level of at least 10%; (iv) increasing fibre levels from D10 to D15 principally obtained by adding 1.5, 3.0, 4.5, 6.0, 7.5 and 9.0% of dried sugar beet pulp, wheat bran and alfalfa; (v) supplementation with 0.5% celite as a marker. Ileal contents were collected every 30rain from 09:00 to 17:00 h, 3 days per week, by free outflow to plastic bags, and pooled daily for each pig before freeze drying. Thereafter, samples were pooled for each diet. Faeces were collected twice per day, frozen immediately, later dried at 60 °C and pooled. Finally, six diets, six ileal and six faecal samples were analysed for CF, NDF, ADF and TDF (Theander and Aman, 1979 ). RESULTSAND DISCUSSION
In vivo experiments Data from the fibre analyses of the six diets and the corresponding pooled ileal and faecal samples are given in Table 1. The CF and NDF levels are quoted as percentages of total dietary fibre (TDF). From comparison of the results, it is clear that the proportions of the various analytical fibre parameters differ between diets and between their ileal and faecal residues. At the dietary level, NDF and TDF are reasonably similar, while CF is 35% of the
FIBREDIGESTIBILITYIN PIGS
57
TABLE 1 Dietary, ileal and faecal fibre contents (% DM ) Diets D 10-D 15 D10
DII
DI2
DI3
DI4
DI5
Dietary samples CF ADF NDF NSP Klason lignin TDF KMnO4 lignin
5.26 8.05 14.87 14.21 1.55 i 5.76 1.65
6.05 10.21 15.81 14.37 1.61 ! 5.98 2.29
6.85 10.07 18.00 16.87 2.05 18.92 4.02
9.63 12.64 21.02 18.91 2.61 21.52 3.38
9.09 13.30 24.07 21.23 3.21 24.44 3.58
8.91 13.30 23.98 19.57 3.19 22.76 3.90
Percent of TDF CF NDF
33.37 94.35
37.86 98.94
36.21 95.14
44.75 97.67
37.19 98.49
39.15 105.36
Ileal samples CF ADF NDF NSP Klason iignin TDF KMnO4 lignin
15.00 21.47 34.50 38.74 4.66 43.40 2.71
14.35 22.57 32.69 34.99 5.37 40.36 2.24
15.55 23.09 34.12 38.87 5.86 44.73 1.99
18.59 28.17 40.27 37.45 7.29 44.74 4.49
18.10 27.29 41.43 44.35 7.04 51.39 3.59
16.16 24.98 37.68 36.26 6.43 42.69 4.86
Percent of TDF CF NDF
34.56 79.49
35.55 80.99
34.76 76.28
41.55 90.00
35.22 80.61
37.85 88.26
Faecal samples CF ADF NDF NSP Klason lignin TDF KMnO4 lignin
21.30 33.21 47.72 30.55 10.74 41.29 6.24
17.18 30.17 40.79 24.82 l 1.42 36.24 5.77
21.50 36.25 45.59 30.01 12.69 42.70 7.68
21.30 36.81 44.86 29.75 17.23 46.98 9.29
20.86 33.33 49.74 30.79 15. ! 5 45.94 7.41
18.16 28.39 38.76 24.44 12.60 37.04 7.46
Percent of TDF CF NDF
51.78 115.57
47.41 112.56
50.35 106.77
45.34 95.48
45.41 108.27
49.03 104.64
CF, crude fibre; ADF, acid detergent fibre; NDF, neutral detergent fibre; NSP, non-starch polysaccharides; TDF, total dietary fibre (NSP + Klason lignin ).
TDF content. Klason lignin contents at ileal and faecal levels exceed the KMnO4 lignin, presumably because of the presence of variable amounts of non-lignin components such as waxes, cutin, tannins and glycoproteins in the former (Graham, 1988 ). At the faecal level, a relatively important decrease
58
I.J. VERVAEKEETAL.
in NSP content and an enrichment of the Klason lignin again changed relative concentrations of the various fibres. Concerning fibre degradation (Table 2), it is noticeable that the ileal apparent degradability values for CF, ADF, TDF and NSP were in the same range for each diet, but lower than the N D F digestibility, probably because of partial solubilization of the NDF fraction in the small intestine. The faecal NSP degradability greatly exceeded the other fibre degradability values and was similar for all the diets, while CF and ADF degradability values differed more among diets. The soluble NSP fraction was enriched by nearly 19% at the ileum and the insoluble NSP fraction degraded by approximately 21% (Table 3 ). This solubilization could possibly lead to an underestimation of fibre degradation capacity in the small intestine if inappropriate methods were used. It is noteworthy that 18% of the total dietary NSP fraction was degraded precaecally. According to Graham ( 1988 ), a significant degradation of some dietary fibres can occur prior to the ileum, probably as a result of bacterial activity, and this should facilitate a more complete digestion of other nutrients in the upper part of the tract. TABLE 2
Ileal and faecal apparent digestibility of fibre (%) DI0
Dll
DI2
DI3
DI4
Dl5
6.1 12.2 23.6 9.4 10.3 65.7
20.8 20.2 30.9 15.6 18.7 65.1
19.4 18.6 32.7 16.0 18.2 62.2
24.1 12.4 24.7 18.2 22.2 58.9
14.8 12.2 26.3 10.0 10.6 56.8
13.8 10.8 25.4 10.9 12.0 53.3
29.8 28.4 45.0 54.6 62.7 85.6
49.2 47.2 53.9 59.5 69.1 84.0
44.6 30.5 55.3 60.2 62.6 83.0
44.0 40.0 56.1 55.1 67.0 81.0
51.3 46.9 56.2 60.1 69.4 79.2
49.3 41.6 55.8 53.0 65.9 74.6
23.7 16.2 21.4 45.2 52.4 19.9
28.4 21.0 23.0 43.9 50.4 18.9
25.2 17.9 22.6 44.2 50.4 20.8
19.9 27.6 31.4 35.9 44.8 22.1
36.5 34.7 29.9 50.1 58.8 22.4
30.5 30.8 30.4 42.1 63.9 21.3
Ileal CF ADF NDF TDF
NSP OM
Faecal CF ADF NDF TDF
NSP OM
Faecal-ileal CF ADF NDF TDF
NSP OM
CF, crude fibre; ADF, acid detergent fibre; NDF, neutral detergent fibre; TDF, total dietary fibre; NSP, non-stareh polysaccharides; OM, organic matter.
FIBREDIGESTIBILITYIN PIGS
59
TABLE 3 Dietary composition and ileal and faecal digestibility (% DM) of soluble (S) and insoluble ( IS ) nonstarch polysaccharides (NSP): comparison of diets DI0 Diet Content
Ileal Content
Digestible
Faecal Content
Digestible
DII
DI2
D13
D14
D15
Mean
SD
S IS Total
2.3 11.9 14.2
2.1 12.3 14.4
2.4 14.5 16.9
2.7 16.3 19.0
2.8 18.4 21.2
3.2 16.4 19.6
S IS Total S IS Total
7.5 31.1 38.7 -11.6 14.4 10.3
6.6 28.4 35.0 -3.6 22.5 18.7
8.0 30.9 38.9 -18.9 24.3 18.2
7.8 29.7 37.5 - 1 5 .0 28.2 22.2
8.6 35.8 44.4 -30.0 16.9 10.6
9.1 27.2 36.3 -34.8 21.1 12.0
-19.1 21.3 17.9
11.6 5.0 5.0
S IS Total S IS Total
1.2 29.4 30.6 90.9 57.4 62.7
1.2 23.6 24.8 89.7 65.6 69.1
1.1 28.9 30.0 91.6 64.8 68.6
1.1 28.7 29.8 91.6 63.7 67.0
1.3 29.5 30.8 90.3 66.0 69.4
1.2 23.2 24.4 89.3 54.2 65.9
90.6 61.9 67.1
0.9 4.9 2.5
The total faecal NSP digestibility was between 62 ( D I 0 ) and 69% (D14). Differences were generally larger at the ileal than at the faecal level, confirming the general statement that ileal results are characterized by a higher variability than faecal data. Table 4 summarizes the dietary levels, ileal and faecal digestibility of the soluble and insoluble NSP monomers. Rhamnose and mannose residues, present in the diets at less than 1%o,are not mentioned. Arabinose, xylose, galactose, glucose and uronic acid concentrations were respectively 2.8, 3.0, 1.4, 6.7 and 2.8% of the dry matter content with a soluble fraction of less than 1%o.The general increase of arabinose and uronic acid residues from D I0 to D 15 is mainly related to the higher beet pulp content. The xylose increase on the other hand originated from a higher wheat bran or cereal level. According to the ileal digestibility data (Table 3) the soluble NSP monomers and particularly the uronic acids, were enriched (negative digestibility ). Soluble glucose, presumably from cereal mixed-linked fl-glucans, was degraded by 50%. The insoluble NSP fraction was degraded by 21%0 in the ileum with the highest level from uronic acids and a lower one from xylose residues. Soluble undegraded monomers are transported to the caecum. At the faecal level, only 10% of each soluble NSP component was recovered, suggesting a non-specific and high fermentative capacity of soluble substrates by the microflora. The
60
I.J. VERVAEKEET AL.
TABLE 4 Non-starch polysaccharides: dietary composition, ileal and faecal digestibility (%) NSP components Arabinose
Xylose
Dietary level (% DM ) Total 2 2.753 (1.86;3.82)
3.02 (4.03;2.42)
lleal digestibility (%) Total 7.034 (-4.4; 14.3)
11.0 (1.8; 19.8)
Faecal digestibility (%) Total 74.7 (70.2, 78.0)
52.9 (44.7; 57.1 )
Galactose 1.41 (1.13;1.99)
9.0 (-9.3; 18)
82.4 (75.1; 89.9)
Glucose 6.76 (5.64;7.84)
Uronic acids 2.80 (1.58;3.65)
Total NSP m 17.53 (14.21;21.33)
24.5 (14.6;32.7)
28.0 (-8.1~ 36.3)
17.9 (10.3;26.3)
59.9 (53.3; 64.1 )
81.8 (76.5: 84.9)
67.1 (62.7; 69.4)
Total NSP (rhamnose and mannose included ). aSoluble and insoluble. ~Mean content of D l 0 - D l 5, with range given in parentheses. 4Average digestion coefficient (DC) with range given in parentheses.
digestibility coefficients of the residues from insoluble non-starch polysaccharide, however, varied from 53% for xylose and 60% for glucose to 75% for arabinose and 82% for the uronic acids. These data suggest that cereal hemicelluloses and cellulose are the most resistant polysaccharides in cereals. From our in vivo experiments (Vervaeke et al., 1989) it was concluded that organic matter degradation in the hindgut occurs principally and very quickly in the caecum and proximal colon. These results were in agreement also with the highest in vitro VFA production rates with inoculum from caecal and colon contents of slaughtered pigs. From these experiments, it can be expected that the transit time of the digesta in the large intestine should be of secondary importance to the total hindgut digestive capacity of carbohydrates, as composition of the undegraded insoluble NSP fraction is apparently the main factor limiting the fermentation; moreover, a lower water activity in the distal segments of the large intestine would tend to limit microbial attack. CONCLUSION
Beet pulp, alfalfa and wheat bran were simultaneously included in six diets at levels from 1.5 to 9.0% each in order to obtain significant differences in ileal and large intestinal digestion. Differences in CF, NDF, ADF and TDF were larger, however, at the ileal and faecal level than at the dietary level. The CF data represent only a small part of the total dietary fibre fraction and
FIBRE DIGESTIBILITY IN PIGS
61
consequently underestimate the fibre digestive capacity of the pig substantially. The NDF and ADF faecal and hindgut digestibility values were substantially lower than the NSP digestibility. The solubilization of non-starch polysaccharides, particularly of uronic acid residues, in the small intestine was apparent. The faecal data show that xylose and glucose polymers are the NSP most resistant to digestion. ACKNOWLEDGEMENTS
This work, which was supported by the IWONL, Brussels, benefited from a fellowship award under an OECD project on Food Production and Preservation.
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